Curling stone

ABSTRACT

A curling stone ( 10 ) having a running surface ( 28 ) is made of a ceramic material. The curling stone ( 10 ) has a base body ( 12 ) and at least one insert part ( 14 ) connected therewith, and the running surface ( 28 ) is formed on the insert part ( 14 ) made of ceramic material. The insert part ( 14 ) is bonded to the base body ( 12 ) by material-fit and/or form-fit and/or force-fit connection.

Curling is a winter sport played on ice, which is similar to Boulesgames and Bocce. Two teams of four players each try to slide theircurling stones closer to the center of a target circle than the opposingteam. Curling is very popular in particular in Canada, Scotland,Scandinavia and Switzerland. Curling is played worldwide by about twomillion athletes and is represented in the Olympic games. Due to theattractiveness of the sport, curling enjoys a very large media presence.Curling is one of the precision sports.

Curling stones have a round, polished form; they normally consist ofgranite and have a handle.

The bottom side of a curling stone is concave, so that the actualsliding, or running, surface of the curling stone is fored as an annularsurface having a width of approximately 6 to 12 mm.

When the curling stone slides over the ice, it collects a thin layer ofwater on the annular surface. This water layer is greater in the frontdue to the rotation of the stone around its vertical axis and the higherpressure on the front side thereof caused by the braking of the curlingstone. Thereby, the friction is reduced in front, resulting in acurvature of the runway.

The curling stone is shifted in its delivery targeted in a slow,rotational movement, so that it does run straight, but describes aparabolic trajectory. This makes it possible to play around an opposingstone. The curvature of the trajectory can be influenced by wiping therunway in front of the curling stone with a curling broom. If the pathin front of a curling stone is wiped, while it moves forward, the curveradius is enlarged and the curling stone runs straighter. In addition tothe curvature, the wiping also influences the runtime of a curlingstone. A wiped curling stone loses speed less quickly and thus covers alarger track.

In particular, the Scots are convinced that curling stones with the bestquality are made from a certain type of granite named “Ailsite.” Thisgranite is mined on Ailsa Craig, a small island off the coast ofAyrshire in Scotland. Due to the scarceness of ailsite, such curlingstones cost up to 1,300 Euro. Many curling clubs use curling stones oflower quality, which are available from about 500 Euro and are made froma granite of lesser value.

The main requirement for a running surface of a curling stone having aconcave running surface is that the water absorption of the granite isas small as possible, since otherwise the sliding properties on ice arechanged. Furthermore, the wear on the running surface should be as lowas possible, since the costs and logistical effort for regrinding arevery high. The grinding costs can amount to about 500

/set of curling stones. Curling stones in playing operation must bereground at least once per season.

Modern high performance curling stones comprise two separate parts,namely a stone main base and an insert part connected thereto, whichdetermines the running surface of the curling stone. The insert partconsists of a higher value material in comparison to the material of thestone main base. The insert part of the known high performance curlingstones is usually made from granite, and can be reground only a fewtimes. If too much material is worn off, then the curling stone is nolonger usable or the insert part is detached from the stone and replacedwith a new insert part.

The principal components of granite are feldspar, quartz and micaminerals. Due to this composition of several minerals of varyinghardness, a minor but undesirable absorption of water is unavoidable oralways present. The Vicker's hardness HV is approximately 850 GPa (Mohshardness 6-7). Due to the composition of several minerals with differentand also relatively low hardnesses, curling stones “in operation” have acertain level of wear, so that a defined grinding—as explainedabove—must be restored regularly.

The specifications stated below are set down in Chapter R2 of the bylawsof the World Curling Federation (WCU Rules of Curling):

-   -   Circular shape,    -   Maximum circumference 36″ (91.44 cm),    -   Minimum height 4.5″ (11.43 cm),    -   Total weight between 38 pounds (US) (17.24 kg) and 44 pounds        (US) (19.96 kg).

The WCF Rules do not, however, stipulate the material from which thecurling stone must be made or the “construction design” thereof.

Curling stones in use up to now have deficiencies due to materialproperties resulting from the use of natural products and productionmethods, which are problematic for use. Essential to good properties ofthe curling stone is a high homogeneity of the raw material used incombination with low wear and constant wear behavior. With a naturalsubstance such as granite, this is not ensured with different miningbatches of the granite. The different sliding properties within acurling stone series make a fair competition impossible. Extremelycritical is the situation of the availability of the only granitecurrently used in the world, which—as mentioned above—is mined on theisland Ailsa Craig off the Ayrshire coast in Scotland. The deposits arelargely exhausted, and equivalent material from other sites is not yetknown. For this reason, the price for this coveted raw material is veryhigh and will rise further. A consequence of this factor is that theprice of the curling stones will rise further due to the scarcity of rawmaterial. It is of critical importance to require a set of eight stoneswith identical properties per sports team, to have consistentconditions. If a curling stone is damaged, then it must be replaced byan equivalent curling stone. But this is very difficult with a naturalproduct, so that it cannot be ruled out that the entire set of eightcurling stones cannot be used. In the foreseeable future a shortage ofsuitable curling stones is therefore to be expected.

Attempts to use other materials such as metals or plastics have not beensuccessful to date, since the property potential deviates too much fromthe granite previously used.

In view of these circumstances the object of the invention is to createa curling stone, with which the sport of curling can be operated asbefore, whereby the deficiencies of the known suggested solutions areeliminated by simple means.

This object is achieved according to the invention in that at least thesliding, i.e. running, surface of the curling stone is composed of ahard-wearing technical ceramic.

Preferred refinements and improvements of the invention of the curlingstone according to the invention are characterized in the dependentclaims.

Surprisingly, it was discovered that technical ceramics can solve theproblems of known is curling stones by preferably forming the runningsurface of the curling stone from an insert part (referred tohereinafter as insert) made of technical ceramics.

The property potential of the technical ceramics is predestined for thisapplication, because thereby a curling stone is created, which is bothhard-wearing and also has good sliding properties. Aluminum oxide forthe insert part has proven to be particularly advantageous with regardto the sliding properties. For this, the good tribological properties ofaluminum oxide have been found to be particularly advantageous, becausethe optimal friction and good wear behavior of aluminum oxide are ofvital importance.

In addition, technical ceramics possess the following good mechanicaland physical properties:

-   -   Average to extremely high mechanical strength (>100 MPa)    -   Very high compressive strength (>1,000 MPa)    -   High hardness (>12 GPa)    -   High corrosion and wear resistance (used as wear-protection        material in mills, mixers, seals etc.)    -   Good sliding properties    -   High density (>2.7 g/cm³)    -   No water absorption    -   High homogeneity of the ceramic body, resulting from technical        material.

It has been shown that these material properties of aluminium oxide arepredestined for use as an insert for curling stones, to replace thegranite used up until now. Due to the greater hardness and good wearbehavior, wear and tear of the sliding surface is extremely low, wherebythe associated problems are solved. Furthermore, the problem of waterabsorption is advantageously eliminated by the aluminum oxide material.

A significant further advantage of technical ceramics for the insertpart is the problem-free permanent availability thereof.

It follows from the above that technical ceramics provide an optimalsubstitute for the previously used granite, whereby with technicalceramics existing problems, as mentioned above, can be solved.

In addition to the use of technical ceramics for the insert part ofcurling stones, the installation of the insert part has vitalimportance. The know-how of a ceramics-oriented construction inconjunction with the use of suitable high-performance adhesives is abasic prerequisite for such a functioning composite system.

The ceramic insert part can be produced in a first process step byisostatic pressing, uniaxial pressing, slip casting, injection moldingor another known ceramic shaping technology. In a subsequent secondprocess step the green parts are processed by green machining to thespecified size. However, the processing may also take place hard-ceramicafter the sintering.

This is followed by a sintering process adjusted to the particularceramic material employed, to which a hard-ceramic finishing process canbe applied next by grinding, lapping or polishing. This is not necessarythe case with Near-Net-Forming.

Different variants are possible when installing the ceramic insert partinto the stone base, for example a granite blank. Thereby the insertpart may be joined to the granite stone base by a form-fitting,force-fitting, chemical or adhesive bonding.

The invention will be further explained hereafter by means of severalexamples, it being understood that the invention is not limited to theseexamples.

EXAMPLE 1 Production of an Insert Part from AL₂O₃-Ceramic, in which theExample is ALOTEC-92 of the Applicant

In a first process step a ceramic body with dimensions 250×250×25 mm isproduced from ALOTEC 92 uniaxial with a pressing force of 2,850 kN and apressing pressure >40 MPa on a axial-press. The green density achievedis >2.00 g/cm³. The green body is further treated in a second processstep in a processing center, to prepare a disk having a diameter of 200mm and a thickness of 35 mm. The disk is then tapered in the center areato 10 mm by means of a jigger to obtain the required annular slidingsurface. In addition, a 12 mm bore hole is introduced into the diskcenter. The sintering is performed at 1,600° C. in the gas furnace understandard sintering conditions (50 h, HZ=1 h). The ceramic body has thefollowing ceramic properties:

-   -   Sintering density: 3,662 g/cm³    -   Hardness (HV5): 12.3 GPa    -   Sound velocity: 9.980 m/s    -   Wear: 0.95 cm³    -   Roughness: R_(A)=1.79, R_(y)=16.24, R_(z)=13.95, R_(q)=2.31

Sliding tests on ice with a curling stone thus prepared gave very goodresults.

EXAMPLE 2 Production of an Insert Part from AL₂O₃-ceramic (ALOTEC-99)

In a first process step a ceramic body with dimensions 220×220×50 mm isisostatically pressed from ALOTEC 99 with a pressing force of 1,000 bar.

The green density obtained is 2.37 g/cm³. In a subsequent second workingstep, a biscuit firing is carried out at 1,100° C., to stabilize thegreen body for further processing steps. The green body is then furthertreated on the jigger to produce a disk having a diameter of 200 mm anda thickness of 35 mm. The disk is then tapered in the center is area to10 mm by means of a jigger, to obtain the required annular slidingsurface. The sintering is performed at 1,620° C. in the gas furnaceunder standard sintering conditions (48 h, HZ=3 h). The ceramic body hasthe following ceramic properties:

-   -   Sintering density: 3.905 g/cm³    -   Hardness (HV5): 16.05 GPa    -   Sound velocity: 10,430 m/s    -   Wear: 0.85 cm³    -   Roughness: R_(A)=0.42, R_(y)=3.43, R_(z)=2.59, R_(q)=0.52

Sliding tests on ice with a curling stone having an insert part thusprepared gave very good results.

Grinding tests were performed on this production example. Aftergrinding, the following roughness values were:

-   -   Roughness: R_(A)=0.03, R_(y)=2.71, R_(z)=1.2, R_(q)=0.09

The sliding properties are still very good. However, the sliding testson ice demonstrate that the disks are “too smooth” for use. When slidingover the ice, a thin water layer accumulates particularly on the annulargliding surface. This thin water layer is greater in the front due tothe rotation of the stone around its vertical axis and the higherpressure on the front side thereof caused by the braking of the curlingstone.

Due to the smooth surface of the ceramic insert part, the desired andnecessary so-called Curl-Effect, i.e. the parabolic curved path, is notadequately achieved.

EXAMPLE 3 OF ANOTHER PRODUCTION AND MATERIAL

3.1) The insert part is glued exactly into the base of the granitecurling stone. For this, an elastic adhesive is used, which must have alow resistance to high temperature. Thereby, by thermal treatment of thecurling stone a damaged or worn insert part can be removed from thecurling stone base and replaced.

3.2) The insert part is glued exactly into the base of the granitecurling stone. For this, an elastic adhesive is used, which has a lowresistance to high temperature in order to prevent the insert part fromfalling out unintentionally, or

3.3) The insert part is combined with a screw, by means of which thehandle is fixed on the top side of the curling stone. With such a designof the latter type, a simpler, easier and time-saving replacement of theinsert part is possible.

In addition to the significantly improved properties of the sliding orrunning surface, these three assembly methods provide an essentialadvantage of the curling stone according to the invention.

Previously, worn, defective curling stones had to be milled again athigh cost, and then were provided with a new insert part made of graniteand thus reconditioned.

According to the invention, rings or disks made from ceramics, hollowceramic bodies, ceramic tubes, ceramic blanks, or one-piece ceramiccurling stones may be used.

The dimensions of the components can naturally be adapted to theparticular requests and/or requirements in a simple manner.

The curling stones can also be manufactured from alternative materials,since the granite supply is increasingly scarce and thus the price forcurling stones made from granite is always higher. According to theinvention, at least the sliding, i.e. running surface, of the curlingstone is composed of technical ceramics as wear-resistant materialshaving the desired sliding properties.

If alternative materials are applied, then the insert part can beselected from ceramics so that the stipulated weight of the curlingstone is obtained. For this purpose it is possible that the curlingstones made from the particular material according to the invention maycomprise, for example, a recess or a pocket for an additional weight toachieve the required total weight of the curling stone. Likewise, it ispossible to provide a recess for an electronic circuit in the curlingstone and/or in the base body thereof.

If the discussion above is always of a curling stone, this does not meanthat it concerns a stone material or granite for the base body, butrather to achieve the desired and/or required properties such as wearresistance and sliding behavior, it can be sufficient if at least thesliding, i.e. running surface, of the curling stone according to theinvention consists of a suitable material.

Further details, characteristics and advantages will be apparent in thefollowing description of exemplary embodiments of the curling stoneaccording to the invention depicted in sectional views.

In the drawings:

FIG. 1 schematically shows a first embodiment of the curling stone,

FIG. 2 schematically shows a second embodiment of the curling stone,

FIG. 3 schematically shows a third embodiment of the curling stone,

FIG. 4 schematically shows a fourth embodiment of the curling stone,

FIG. 5 schematically shows a fifth embodiment of the curling stone,

FIG. 6 schematically shows a sixth embodiment of the curling stone,

FIG. 7 is a sectional view of an embodiment of the curling stone similarto the embodiment having two annular insert parts shown in FIG. 1,

FIG. 8 is a sectional view of a curling stone having an annular insertpart, which surrounds a central base body,

FIG. 9 is a sectional view of a curling stone similar to the curlingstone according to FIG. 8 having an annular insert part with aunilaterally enlarged running surface.

FIG. 10 is a sectional view of a curling stone having two disk-shapedinsert parts, between which a disk-shaped base body is provided,

FIG. 11 is a sectional view of a curling stone similar to the embodimentdrawn schematically in FIG. 3,

FIG. 12 is a sectional view of a curling stone similar to the embodimentdrawn schematically in FIG. 4.

FIG. 13 is an embodiment of the curling stone having two disk-shapedinsert parts facing opposite to each other, wherein the base body isdesigned with a receiving compartment,

FIG. 14 is a sectional view of the curling stone having two disk-shapedinsert parts facing opposite each other—similar to the embodimentaccording to FIG. 13—and with an additional annular ceramic body on theexternal circumferential surface of the curling stone.

FIG. 1 schematically illustrates an embodiment of the curling stone 10,which has a base body 12 made, for example of granite, and an insertpart 14 made of ceramic material. The insert part 14 glued into a recessof the base body 12 forms the running surface of the curling stone 10,the base body of which is depicted as simply planar and not with aconcave base.

FIG. 2 shows an embodiment of the curling stone 10, which instead of anannular insert part 12 as depicted in FIG. 1, has an insert part 14formed as a blank from ceramic material.

FIG. 3 illustrates an embodiment of the curling stone 10 having a basebody 12 and an insert part 14. The insert part 14 is designed as a diskmade of ceramic material, which is glued into a recess in the base body12.

FIG. 4 shows a curling stone 10, which consists entirely of a ceramicmaterial, to accomplish the desired sliding and wear properties.

FIG. 5 shows an embodiment of the curling stone 10, which consists ofceramic material and which has an annular insert part 14 and a pocket 16for a ballast weight and/or for an electronic circuit.

FIG. 6 illustrates an embodiment of the curling stone 10 having anannular insert part 14 and a base body 12 made from an alternativematerial 12 and an outer ring body 18, which encloses the base body 12.

FIG. 7 illustrates in a sectional view an embodiment of the curlingstone 10 having a base body 12, which is designed with a centralthrough-hole 24 between the concave bottom 20 and concave top 22thereof. The bottom 22 and top 22 are the same shape, so that thecurling stone 10 can be inverted if necessary and the top 22 can be usedas the bottom 20 of the curling stone 10. The bottom 20 and the top 22are respectively designed with an annular recess 26. In each recess 26an annular insert part 14 is screwed-in or glued, which determines arunning surface 28 of the curling stone 10.

The base body 12 can consist of natural stone. The natural stone can begranite, for example. However, the base body 12 can also comprise metal,glass or wood. Likewise it is possible that the base body 12 maycomprise a plastic material and that in the production of the curlingstone 10 the insert part 14 is directly and immediately overmolded andpermanently joined with the plastic material of the base body.

FIG. 8 illustrates in a sectional view an embodiment of the curlingstone 10 having a central base body 12 and an annular insert part 14made of ceramic material enclosing the base body 12, which determinesthe running surface of the curling stone 10.

Identical details are denoted in FIG. 8 using the same referencenumerals as in FIG. 7, so that it is not necessary to repeat all detailsfor FIG. 8.

With the embodiment according to FIG. 8, it is also possible to use theconcave top 22 as the bottom 20 of the curling stone 10 at a given timeand in this way to extend, i.e. double, the operative, i.e. use time, ofthe curling stone 10.

FIG. 9 shows in a sectional view one of the embodiments of the curlingstone 10 similar to that of FIG. 8, wherein the annular insert part 14made of ceramic material enclosing the central base body 12 is designedwith an annular circumferential collar 30 to enlarge the running surface28 of the curling stone 10.

FIG. 10 illustrates in a sectional view an embodiment of the curlingstone 10 having a disk-shaped base body 12, which is combined on the topand bottom, respectively, with insert parts 14 made of ceramic material,each of which are also designed disk-shaped. One disk-shaped insert part14 is designed with a concave base body 20 and the other disk-shapedinsert part 14 facing away therefrom is formed with a conformal, concavetop side 22, so that the curling stone 10 can be used either with itsconcave bottom side 20 or, after pivoting 180°, with its top side 22 asbottom side 20. The two disk-shaped insert parts 14 can be glued to thebase body 12. Likewise it is possible to screw the two disk-shapedinsert parts 14 together to the base body 12—and to a handle which isnot shown—through the central through-hole 24.

FIG. 11 illustrates in a sectional view an embodiment of the curlingstone 10 similar to the embodiment schematically drawn in FIG. 3—havinga base body 12 and an insert part 14 made of ceramic. The insert part 14is provided on the bottom 20 of the curling stone 10 and glued into arecess 26 of the base body 12 or to the base body 12 and a handle whichis not shown or, for example, screwed in through the centralthrough-hole 24.

FIG. 12 shows in a sectional view an embodiment of the curling stone 10similar to the embodiment schematically illustrated in FIG. 4, whereinthe entire curling stone 10 consists of a suitable ceramic material.

FIG. 13 illustrates in a sectional view an embodiment of the curlingstone 10 having an annular base body 12 and two oppositely facing insertparts 14 made of a suitable ceramic material. The base body 12 isdesigned with a central receiving compartment 32, which is axiallydemarcated and enclosed on the top and bottom by the disk-shaped insertpart 14 made of ceramic material. The receiving compartment 32 isdesigned for at least one additional weight, for example to achieve therequired total weight of the curling stone 10 with a relativelylight-weight base body 12, e.g. made from wood or plastic. At least oneelectronic circuit or the like can be provided in the receivingcompartment 32.

FIG. 14 shows in a sectional view an embodiment of the curling stone 10having a base body 12, which is combined on the top and bottom side,respectively, with a disk-shaped insert part 14 made of ceramicmaterial. One insert part base body 14 forms the concave bottom side 20and the other insert part 14 forms the conformal, concave top 22 of thecurling stone 10, which can form, if necessary, the bottom side 20 andthereby the annular running surface 28 of the curling stone 10.Furthermore, in this embodiment of the curling stone 10, the base body12 is combined with an annular ceramic body 34, which defines theexternal covering surface 36 of the curling stone 10.

The same details are each designated with the same reference numerals ineach of FIGS. 1 to 14, so that it is not necessary to describe alldetails in connection with each Figure in detail.

LIST OF REFERENCE NUMERALS

-   10 Curling stone-   12 base body (of 10)-   14 insert part (of 12)-   16 recess/pocket (in 12)-   18 outer ring body-   20 concave bottom side (of 10)-   22 concave top side (of 10)-   24 central through-hole (between 20 and 22)-   26 recess (in 12 for 14)-   28 annular running surface (of 10)-   30 collar (of 14 for 28)-   32 receiving compartment (in 10)-   34 ceramic part (of 10 in 36)-   36 external covering surface (of 10)

1-11. (canceled)
 12. A curling stone having a running surface, whereinthe running surface comprises a ceramic material.
 13. A curling stoneaccording to claim 12, comprising: a base body; and an insert partconnected with said base body; wherein the curling stone has a runningsurface; wherein the running surface is formed from the insert part andis made of ceramic material, wherein the at least one insert part isbonded to the base body by a material-fit, and/or form-fit and/orforce-fit connection.
 14. A curling stone according to claim 13, whereinthe insert part comprises an oxide ceramic material.
 15. A curling stoneaccording to claim 14, wherein the at least one insert part is composedof an aluminum oxide ceramic.
 16. A curling stone according to claim 14,wherein the at least one insert part is composed of a mixed ceramicmaterial.
 17. A curling stone according to claim 13, wherein the basebody is designed with a recess for the corresponding insert part.
 18. Acurling stone according to claim 17, wherein the insert part is fixed inthe corresponding recess of the base body with use of a glue.
 19. Acurling stone according to claim 17, wherein the insert part is fixed inthe corresponding recess of the base body by means of ascrew-connection.
 20. A curling stone according to claim 19, wherein thescrew connection is provided at the same time for fixing in place ahandle projecting from the curling stone.
 21. A curling stone accordingto claim 12, wherein the base body is composed of natural stone,preferably granite, or an alternative material such as metal, glass,plastic or wood.
 22. A curling stone according to claim 12, wherein thebase body comprises at least one receiving compartment or at least onepocket and/or at least one storage compartment for at least oneelectronic circuit.